1. Field of the Invention:
The present invention relates to a press for separating liquid from a two-phase solid-liquid material, and more particularly to a double-screw expeller for expressing vegetable oil from seeds.
2. Description of the Relevant Art:
Apparatus for expressing oil, water, and other liquids from various materials such as vegetable seeds, e.g., sesame seeds and sunflower seeds, animal meat by-products, starch, etc,, are generally classified into batch presses and continuous presses. The batch presses include cage presses and filter presses. These batch presses are mainly used to manufacture a Japanese alcoholic beverage known as "sake" and soy sauce since they can separate clear high-quality liquids from the material using cloth filter bags. Typical continuous presses are roller mills. In a roller mill, since the material from which a liquid is to be separated is pressed under a relatively low pressure, a large amount of liquid remains in the cake after expression by the roller mill. Therefore, use of the roller mills is primarily limited to dewatering of starch.
Another form of continuous press is a screw press which is particularly suitable for expressing vegetable oil from oilseeds. One typical screw press comprises a barrel and a screw closely fitted in the barrel. The barrel may comprise a cylindrical barrel having a multiplicity of holes or a drainage barrel having slits extending along the screw with spacers therebetween. In the screw press, the seeds from which oil is to be expressed are fed forward by friction with the inner circumferential surface of the barrel. In order for the seeds to be moved by friction, their protective shells, known as testa, must be left uncrushed. The materials that can be processed by the screw press are therefore limited to oil seeds and materials with high fibrous content. Oil which is expressed by the screw press should be refined because it contains testa. However, the refining process is costly and laborious. Other problems of the screw press are that the barrel are rapidly worn by frictional contact with the material and the material tends to be modified in property due to frictional heat.